Command Reference Guide

3Com Router 5000 Family and Router 6000 Family bridge stp timer forward-delay ● 27
Command Reference
bridge stp timer forward-delay
Purpose Use the bridge stp timer forward-delay command to set the Forward
Delay timer on the bridge.
Use the undo bridge stp timer forward-delay command to restore the
default.
Syntax bridge stp timer forward-delay seconds
undo bridge stp timer forward-delay
Parameters seconds
Value for the Forward Delay timer on the bridge. Valid
values are 4 to 200 seconds.
If no value is specified, the default value is 15 seconds.
Example Set the Forward Delay timer on the bridge to 50 seconds.
[Router] bridge stp timer forward-delay 50
View This command can be used in the following views:
■ System view
Description A link fault on the network may cause a spanning-tree recalculation immediately;
however, it takes time for the new BPDU to propagate throughout the entire
network. If new root ports and designated ports start forwarding frames immediately
after they are elected, a temporary loop may occur.
To resolve the problem, STP adopts a state transition mechanism, where a root or
designated port must undergo a transitional state before it enters the forwarding
state to forward frames. The duration of this transitional state depends on the setting
of a timer called Forward Delay timer. It ensures that the new BPDU has been
propagated throughout the network before frames are forwarded according to the
latest topology.
When configuring a Forward Delay timer, consider the following:
■ On a spanning tree, all bridges must use the Forward Delay timer of the root bridge
instead of their own.
■ Use the default Forward Delay timer setting if possible. A small forward delay may
create temporary path redundancy; while a large forward delay may increase the
time required for the topology of the spanning tree to converge. In the latter case,
network connectivity recovery may take a long time.